Impl Send+Sync for every trait, not just those with it explicit

Impl Send+Sync for every trait, not just those with it explicit

Because Send+Sync are generated by the compiler for us, we don't
really know when we should or should not generate it. That said,
Send+Sync aren't exposed outside of Rust, so it only impacts
whether we can use a type when passed to Rust, not how users will
ultimately interact with types.